Performance of a semiconductor integrated circuit may depend on manufacturing processes to manufacture semiconductor devices in the semiconductor integrated circuit. Two neighboring semiconductor devices manufactured by a same process are supposed to have the same characteristics and/or behave in a same manner. Because of manufacturing process variations, however, characteristics and behaviors of the two semiconductor devices may not be the same.
Generally, a semiconductor integrated circuit requires high circuit performance and high density. Therefore, in the case of a semiconductor device, e.g. a metal oxide semiconductor field effect transistor (or “MOSFET”), the technology for the forming a semiconductor integrated circuit has been scaled down to a sub-micron range as a result of the efforts to reduce the size of the MOSFET device. A lightly doped drain (or “LDD”) structure is adopted in a MOSFET device to mitigate hot carriers injection (or “HCl”) that adversely affects the reliability of the MOSFET device.
Random dopant fluctuation (or “RDF”) resulting from the process of forming an LDD structure in a MOSFET device can alter the MOSFET device's properties, especially threshold voltage. Due to the variation of RDF, a mismatch between threshold voltages of the two transistors exists.